Apparatus for spindle bearing friction estimation for reliable disk drive startup

ABSTRACT

Temperature of the disk drive is measured using components of the disk drive without the need of including a separate temperature sensor to optimize performance of the spindle motor during startup. To measure temperature, the resistance of the VCM winding is measured and used to estimate the spindle bearing temperature. Back emf is measured from VCM windings and used during startup to accurately determine actuator position. Because the VCM coil resistance varies significantly with temperature, coil resistance variations with temperature are determined to enable compensation for inaccuracies in determination of actuator velocity. This inferred temperature is then used to optimize the start up procedure for the spindle motor to accommodate the increased frictional loading of the spindle bearing. In this way an improved performance in the reliability and spin up operation time can be realized without the addition of a separate temperature measurement hardware element.

PRIOITY CLAIM TO PROVISIONAL APPLICATION

This patent application claims priority to U.S. Provisional PatentApplication No. 60/436,750, filed Dec. 27, 2002.

BACKGROUND

1. Technical Field

The present invention relates to a method for starting a brushless DCspindle motor in a hard disk drive memory subsystem, and moreparticularly to starting the spindle motor in the presence of varyingambient temperatures.

2. Related Art

A hard disk drive typically includes one or more rotatable storagemedia, or disks upon which data is encoded. The disks are mounted on theshaft of a spindle motor for rotation. Data is encoded on the rotatingdisks as bits of information using magnetic field reversals grouped intracks. A transducer head supported by an actuator arm is used to readdata from or write data to the disks. A voice control motor (VCM)attached to the actuator arm controls positioning of the actuator, andthus the transducer head position over a disk. Servo position data readfrom the disk is processed by the processor, enabling the processor toprovide servo control signals to the VCM for proper positioning of atransducer head relative to a disk.

Temperature changes during startup can significantly affect componentsof the disk drive. The operating temperature of a drive can be up to 50degrees Celsius higher than the drive when it first starts at roomtemperature. In particular, low temperatures at startup of the drivewill significantly affect run-up of the spindle motor. Oil bearingspindles, or other hydrodynamic spindle motors, have increased dragtorque at low temperatures, primarily due to increased viscosity of thebearing fluid. The increased drag is most significant for hydrodynamicbearing spindles, which may be used in very high speed hard disk drives,such as drives that operate at 10,000 revolutions per minute (rpm).

A specific disadvantage is that the increased drag of the spindlebearing at low temperature start conditions may be so high that thespindle does not come up to speed in a desired time. For a 10,000 rpm,hydrodynamic bearing spindle, the difference in power due to additionalbearing drag can be 1.0 Watt between 10° C. and 25° C. This correspondsto a significant difference in drag torque. A spindle motor with atorque constant based upon this worst case start condition maysignificantly compromise the motor at nominal operating conditions. Theincreased drag at low temperature starts would demand a lower torqueconstant to meet necessary voltage headroom conditions. A typical designpractice is to reduce the motor torque constant just enough to allowspindle motor spin-up within a desired time, while allowing sufficientvoltage headroom for adequate speed control.

The spindle motor bearings in typical disk drive spindle motors arelocated very close to the motor windings. The motor windings are themost significant source of heat in a motor. Thus, as the motor starts,the bearings heat up and increase in temperature. The bearing dragtorque is a function primarily of the viscosity of the bearing greasebase oil and of the stiffness of the grease, both of which reduce withincreased temperature. So the bearing drag torque reduces with timeshortly after the motor starts spinning due to the heating of thebearings. By allowing more time to spin up to speed before closed loopmotor control takes over, the bearing drag can be reduced.

An error checking procedure for the proper operation of disk drives,primarily magnetic disk drives, is to conduct a “time out test” at thestart-up of the disk drive. In a time out test, if the disk drive doesnot reach full operational speed within the time out or specifiedperiod, it is deemed an error. Often, a spindle motor controller sendsan error signal if the spindle motor cannot come up to speed during thetime out period and the drive is turned off.

SUMMARY

In accordance with the present invention, a method of measuringtemperature of the disk drive and use of the temperature to controlspin-up of the spindle motor is provided using components of the diskdrive without the need of installing a separate temperature sensor.

To determine temperature, the resistance of the VCM coil winding ismeasured and used to estimate the spindle bearing temperature. Back emfmeasurements determined from VCM coil winding are typically used duringstartup to accurately determine actuator velocity and position. Becausethe VCM coil resistance varies significantly with temperature, coilresistance variations with temperature are determined to enablecompensation. The tabulated temperatures are in turn used, in accordancewith the present invention, to infer temperature of the drive duringstartup. This inferred temperature is then used to optimize the startprocedures for the spindle motor to accommodate the increased frictionalloading of the spindle bearing. In this way an improved performance inthe reliability and spin up operation time can be realized without theaddition of a separate temperature measurement hardware element.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details of the present invention are explained with the help ofthe attached drawings in which:

FIG. 1 shows a block diagram of components of a hard disk driveconfigured to provide a disk drive temperature estimation duringstart-up based on measured resistance of the VCM coil; and

FIG. 2 shows details of the VCM driver of FIG. 1; and

FIG. 3 shows details of the spindle motor, along with further details ofthe spindle motor driver circuit shown in FIG. 1.

DETAILED DESCRIPTION

FIG. 1 shows a block diagram of components of a hard disk drive systemconfigured to provide a disk drive temperature estimation duringstart-up. The hard disk drive includes a rotating disk 2 containing amagnetic medium for storing data in defined tracks. Data is written toor read from the disk 2 using a transducer or read/write head 4 providedon an actuator 6. Actuator movement is controlled by a voice controlmotor (VCM) 7 made up of a coil configured for receiving an externalsignal, and a rotor magnet.

Current is provided to the coil of the VCM 7 using a VCM driver 10.Details of the VCM driver 10 and VCM 7 are described subsequently withrespect to FIG. 3. The VCM driver 10 in turn receives positioningcommand signals from a processor 12 to control the amount of currentapplied to achieve a desired movement of actuator 7.

To control the actuator 6 using a closed loop servo control technique,the processor 12 receives data from the rotating disk 2. The data isread from or written to the rotating disk 2 using the transducer head 4.The analog data read is provided through a read/write (R/W)pre-amplifier 14. The amplified read data is provided to the R/W channel16, which includes circuitry to convert the data from analog to digitaland decode the digital data to provide to the hard disk controller (HDC)34. The R/W channel 16 further converts data received from the HDC to bewritten from digital to analog for providing through the R/W preamp 14to transducer head 4. The data read includes servo data provided indigital form from the HDC 34 to the processor 12.

Servo data provided to the processor 12 includes information indicatingtrack positioning of the transducer head 4 over the rotating disk 2. Theprocessor 12 determines track mis-registration (TMR) and creates a servopositioning control command signal for providing to VCM driver 10 tocorrect for the TMR. Also, if it is desired to read data from or writedata to other tracks on the rotating disk 4, the processor 12 createsservo positioning control commands for providing to VCM driver 10 toenable the transducer head 4 to move from the current track to thedesired track.

The processor 12 can provide control commands to a spindle motorcontroller 18 to control the operation speed of the spindle motor. Thespindle motor controller 18 in turn provides control signals to thespindle motor driver 19, which in response applies voltages to thewindings of the spindle motor to cause the desired motor speed. Thespindle motor driver 19 is described in more detail subsequently withrespect to FIG. 3.

Processor 12 executes instructions acquired from a stored controlprogram to control disk drive functions. During startup, the controlprogram is embedded in flash memory, or other non-volatile memory andthen either executed directly, or loaded into a random access memory RAM22 connected to the processor 12 and executed. Various firmware routinesare stored in memory locations for controlling the operation of theactuator 7 and spindle motor 30. Here, control programs include theinstructions the processor 12 executes, and tables, parameters orarguments used during the execution of these programs.

The processor 12 also communicates with the HDC 34 which has access tocomponents external to the hard disk drive system through an advancedtechnology attachment (ATA) interface bus 20. The ATA bus 20 is alsoreferred to as an integrated drive electronics (IDE) bus, and althoughspecifically shown as an ATA bus, may be another type of externalcomponent interface in accordance with the present invention. The HDC 34further provides access to additional DRAM memory 36. Control programsfor the processor may reside in DRAM 36, or in RAM 22 directlyaccessible by the processor 12.

For a hard disk drive, application specific integration circuits (ASICs)have been created to integrate a number of circuit components onto asingle chip. One such ASIC 26 is illustrated in FIG. 1. As shown, theASIC 26 integrates the processor 12, RAM 22, R/W channel 16, spindlemotor controller 18, HDC 34, DRAM 36, and ATA interface bus 20 all ontoa single chip. The chip for disk drive control is typically referred toas a system on a chip (SOC).

Although shown as separate components, the VCM driver 11 and spindlemotor driver 19 can be combined into a single “hard disk controller”.The processor 12 is shown as a single unit directly communicating withthe VCM driver 10, although a separate VCM controller processor may beused in conjunction with processor 12 to control the VCM driver 10.Further, although spindle motor controller 18 is shown as a separateprocessor from processor 12, it is understood that the spindle motorcontroller 18 may be combined into the processor 12.

FIG. 2 shows details of the VCM driver 11 of FIG. 1 as connected to theVCM 7. As shown, the VCM driver 11 includes a VCM current applicationcircuit 50, which applies current to the coil 8 of the VCM 7 with aduration and magnitude controlled based on a signal received from theVCM driver 10. The coil 8 is modeled in FIG. 3 to include a coilinductance 71, a coil resistance 72 and a back emf voltage generator 73.Current provided through the coil 71 controls movement of the rotor 9,and likewise movement of the rotor generates a back emf voltage involtage generator 73.

The VCM driver 10 further includes a back emf detection circuit 52 forsensing the velocity of the actuator based on current received by asense resistor 70 in the VCM 7. The open-circuit voltage of the VCM isestimated by observation of the actual VCM voltage and the VCM current(either the commanded current or the sensed current, sensed using aseries resistor 70), and multiplication of the current by an estimatedVCM coil resistance and subtraction of that amount from the measuredcoil voltage.

During startup, actuator velocity is determined using measurements fromthe VCM back emf detection circuit 52. To monitor the actuator velocity,back emf voltage across the coil 8 of the VCM 7 is monitored as part ofthe voltage of the actuator. Back emf varies as a function of thevelocity of the actuator coil through the magnetic field produced by themagnet 9 of the VCM 7 and as a function of the velocity of the actuator6 down the ramp 28. Servo indications on the disk can be read when aspindle motor normal operation speed is obtained after spin-up.

The current application circuit 50 can function as a processor todetermine the appropriate amount of current to apply to windings of theVCM 7 to achieve a desired movement, or simply as a circuit to applyvoltages with processing performed by processor 12. With currentapplication circuit 50 acting as a processor, feedback from the back emfdetection circuit 52 is provided to the current application circuit 50to enable a determination of actuator movement during startup, andappropriate current to apply to achieve a desired actuator movement. Themain processor 12 only functions to send control codes to indicatemovement should occur to a desired position. With the currentapplication circuit limited to circuitry for applying voltages, and allprocessing performed by processor 12, a feedback signal from the VCMback emf detection circuit 52 will be provided to the processor 12 toenable the processor 12 to determine actuator velocity at startup andapply appropriate control signals to the VCM current application circuitto achieve a desired actuator movement.

As indicated previously, during shut down, the actuator 6 is positionedon a ramp 28 situated off to the side of a disk 2 to prevent contactbetween the transducer head 4 and disk 2. During startup, actuatorvelocity down the ramp 28 is controlled using measurements from the VCMback emf detection circuit 52 so that the slider of transducer 4 flieswhen it gets to the bottom of the ramp 28 and does not contact the disk2. The slider has an air bearing surface that causes the transducer tofly above the data tracks of the disk surface due to fluid currentscaused by the spindle motor rotating the disk. Thus, the transducer 4does not physically contact the disk surface 2 during normal operationof the disk drive to minimize wear at both the head 4 and disk surface2. With contact of the transducer head 4 and disk surface 2 undesirable,a critical time during operation of a disk drive is just before the diskdrive shuts down. When shutting down a disk drive, the actuator 6 ismoved so that the transducer 4 does not land on the portion of the diskthat contains data. How this is actually accomplished depends on thedesign of the drive.

Typically during shut down, the actuator 6 is positioned on a ramp 28situated off to the side of a disk 2. A portion of the ramp 28 ispositioned over the disk 2 itself. In operation, before power isactually shut off, the actuator 6 assembly slides up the ramp 28 to apark position at the top of the ramp 28 so that the transducer 4 doesnot contact the disk 2. This procedure is known as unloading the heads.

Temperature changes during startup can significantly affect calculationsof actuator velocity based on back emf. The voltage of the actuatormotor varies with the temperature of the permanent magnet 9 and theresistance of the coil 8 in the VCM 7. With operating temperature of adrive up to 50 degrees Celsius higher than the drive temperature when itfirst starts, a resulting change in back emf can be as much as 10–15%.Variations of coil resistance with temperature may thus be determined tocorrect for variations in measured voltage of the actuator motor toestimate the back emf voltage. Since, the material and length of coil 8are known, its resistance variation with temperature is readilydetermined.

Processor 12 executes instructions acquired from a stored controlprogram to control disk drive functions. During startup, the controlprogram is embedded in flash memory, or other non-volatile memory andthen either executed directly, or loaded into RAM 22 and executed.During startup, the control program causes the processor 12 to measurethe back emf from the VCM coil winding 8 to determine velocity of theactuator. In accordance with the present invention, the control programfurther causes the processor 12 to measure either a resulting voltage orcurrent return from VCM coil 8 during the back emf measurement using theVCM back emf circuit 52 to determine a resistance R of the coil 8 basedon the formula V=I×R, where I is current and V is voltage across thecoil 8. The resistance measured can be the resistance of the coil 72, orin other embodiments the resistance of sense resistor 70 or acombination of resistances 70 and 72. The control program then eitheraccesses a table of values to determine drive temperature based on thevalue R, or simply make a calculation to determine drive temperaturebased on the known length, size, and material of the coil 8. Thetemperature measurement is then used to correct the determination ofactuator velocity based on back emf measurement, as well as to optimizespin up of the spindle motor.

FIG. 3 shows details of the spindle motor 30 including coils 62 androtor 68. Also shown are more details of the spindle motor drivercircuit 19 as shown in block diagram in FIG. 1. The spindle motor 30includes three windings 63, 64 and 65 electrically arranged in a Yconfiguration. A rotor 68 supports rotor shaft 31 of the spindle motor30 and has magnets that provide a permanent magnetic field. The spindlemotor 30 generates torque on rotor 68 when current flows through atleast one of the windings 63–65. The torque depends upon the magnitudeand direction of current flow through the windings 63–65, and theangular position of rotor 65 relative to windings 63–65. The functionalrelationship between torque and current flow and angular position iscommonly determined corresponding to a respective one of a series ofcommutation states.

Spindle motor driver 19 supplies current to windings 63–65 to causerotor 38 to rotate at an operating spin-rate during the operation modeof the disk drive. Spindle motor driver 19 includes a commutationcircuit 40 to apply different commutation state currents at differentclock times. Commutation circuit 40 provides a sequence of commutationstates by applying a voltage +V across a selected combination ofwindings 63–65 to generate a torque on rotor 68 in order to maintain theoperating spin-rate of rotor 68.

The commutation circuit 40 clocks a series of commutation clock pulsesapplied to windings 63–65 to advance commutation state from a presentcommutation state to a next commutation state. The series of commutationclock pulses have a corresponding series of commutation clock periods.The commutation clock periods have a systematically introduced variationfrom a nominal commutation clock period that depends on the operatingspin-rate of rotor 68.

Processor 12 executes instructions acquired from a stored controlprogram to control disk drive functions. These functions includestarting up and controlling the speed of spindle motor 30 via spindlemotor controller 19 and numerous other disk drive functions. Spindlemotor controller 19 is connected to processor 12 to permit processor 12to directly communicate with spindle motor driver 19.

Processor 12 suitably includes a flash memory, or other embeddednon-volatile memory that stores control programs it uses during startup.Various firmware routines are stored in memory locations for controllingthe operation of spindle motor 30. Here, control programs include theinstructions the processor 12 executes, and tables, parameters orarguments used during the execution of these programs. Processor controlprograms may also reside in RAM 22, or memory over ATA bus 20.

Spindle motor controller 18 includes a control circuitry to commandspindle motor driver 19 to apply a current through at least one windingof windings 63–65 to cause rotor 68 to rotate. The spindle controller 18executing a speed controller routine controls the current throughwindings 63–65 in order to maintain the operating spin-rate of rotor 68in response to back emf signals received from back emf detection circuit42 in the spindle motor driver 19. The spindle motor controller 19monitors the time period between back emf zero crossings and providesthis time period information to enable determination of the speed ofspindle motor 68. The speed indication is then used to control thecurrent through windings 63–65 to accomplish a desired speed.

Spindle motor controller 18 also controls speed using a series ofcommutation clock pulses to be provided from the commutation circuit 40of the spindle motor driver 19 to advance commutation state sequencefrom a present commutation state to a next commutation state in thecommutation state sequence.

During the operation mode of the disk drive, the commutation statesproceed through a sequence of six commutation states corresponding to aset of torque values to maximize the peak positive torque produced byspindle motor 30. For each of the commutation states, a voltage +V isapplied across a combination of at least two of the windings 63–65.

The spindle motor controller 18 serves as a speed controller to controlthe spin-rate of spindle motor 30 to maintain a substantially constantspin-rate of disk 2. Commutation state sequences are provided ascontrolled by the spindle controller 19 from the commutation circuit 40during the operation mode in response to commutation clock pulses fromthe spindle motor controller 18 so that a desired torque is generatedfor rotor 68 of spindle motor 30.

Although the spindle motor driver 19 and spindle motor controller 18 aredisclosed as separate items, the processing performed can be combinedinto the commutation voltage/timing application circuit 40 to form onedevice. With such a combination, spindle motor back emf detectioncircuit 42 will provide a signal directly to the commutation circuit 40to enable determination of commutation currents needed to achieve adesired speed. With spindle motor controller 18 and driver 19 separated,the spindle motor back emf detection circuit 42 output will go to thespindle motor controller 18.

In accordance with the present invention, the temperature determinedfrom the resistance of the coil windings can be used to optimize spindlemotor performance during startup in a number of ways. In a firstembodiment, the time-out time period for the spindle motor is extendedas temperature is reduced. As indicated above, the time-out period isset to give the spindle motor adequate time to spin-up and reach adesired operation spin rate. If the time-out period is exceeded, asignal is sent from the processor 12 to the spindle motor controller 18to cause the spindle motor 30 to shut down to prevent damage. Withbearing friction significantly increasing with reduced temperature,spin-up time likewise will be significantly increased. Increasedtime-out periods are set corresponding to decreasing temperatures andstored in the start up code accessible by the processor 12. Thus, uponstartup the processor will determine temperature from the VCM coil 8,and then set the time-out period for the spindle motor 30 accordingly.

In another embodiment, the voltage applied to coil windings 63–65 of thespindle motor 30 are increased to generate additional torque during thealignment step and the run up of the startup operation as temperature isreduced. As indicated above, the magnitude of the voltage applied to thecoil windings 63–65 is related to the amount of torque generated by thespindle motor 30. With bearing friction significantly increasing withtemperature, spin-up time can be minimized by increasing the torqueapplied corresponding to a reduction in temperature. Thus, upon startup,the processor will determine temperature from the spindle coilresistance, and then control the spindle controller 18 to set theinitial voltage values to increase torque based on the drive temperaturefor the alignment step and the subsequent run up step. Since the spindlemotor 30 heats up within a matter or minutes, the voltages applied canthen be reduced to level used during normal operation temperatures toprevent damage to the spindle motor.

In an additional embodiment, current magnitude applied to the spindlemotor windings is monitored and current is increased to increase torquewhen temperature levels decrease. Current applied to the spindle motorwindings is then increased as temperature levels rise.

In a further embodiment, the commutation state sequence timing iscontrolled to increase torque during startup as temperature is reduced.As indicated, a series of commutation clock pulses are provided tocontrol application of voltages to the coil windings 63–65. Uponstartup, the processor can determine temperature from the resistance ofthe spindle coil windings 63–65, and then control the spindle controller18 to set the initial commutation states to generate a torque withincreasing value based on reduced drive temperature. As with control ofthe magnitude of the currents, the commutation clock pulses are alteredto increase torque initially upon startup with cold temperatures, butwith the spindle motor 30 heating up to a normal operating temperaturewithin a matter of minutes, the commutation clock pulse periods arereturned to normal to maintain an optimal torque applied to the spindlebearings.

In further embodiments, a combination of controlling the time-outperiod, the currents or voltages applied to the coil windings 63–65 andthe commutation state sequence timing is applied to optimize startup ofthe spindle motor based on startup drive temperature determined from theVCM coil resistance. Such embodiments will combine the features based ondesired design requirements. For instance if the currents used are at amaximum value and cannot be increased during startup, and the time-outperiod can only minimally be increased, a combination of increasingstart-up time and adjusting commutation sequence timing can be used tooptimize startup procedures.

In some circumstances, the spindle motor is shut down without parkingthe actuator on a ramp. Instead the heads land on the disk in a landingzone where data is not stored. During a contact startup operation, atpower up of the disk drive, the head will still be in contact with thelanding zone. A phenomenon known as “stiction” between the head and thelanding zone is a potential problem in a contact start operation.Stiction resists separation between the head and disk surface and can behighly detrimental to disk drive operation. The stiction between thedisk surface and the head can be so significant that a significanthigher spindle motor torque is required to separate the head from thedisk surface, than when the heads are parked on a ramp, or significantlymore time is required for spin-up of the spindle motor. Without parkingthe heads, in accordance with the present invention, startup proceduresmay be altered to increase the time-out period or startup torque toaccount for the increased friction if the heads are not parked on aramp, but instead remain in contact with the disk in combination with alowered temperature.

Although the present invention is described for use with hard diskdrives for recording in magnetic media, it is understood that principlesin accordance with the present invention can be used with optical diskdrives, or other types of magnetic disk drives such as floppy drives.

Although the present invention has been described above withparticularity, this was merely to teach one of ordinary skill in the arthow to make and use the invention. Many additional modifications willfall within the scope of the invention, as that scope is defined by thefollowing claims.

1. A disk drive comprising: a rotatable disk; an actuator that supportsa transducer; a voice control motor (VCM) including a coil windingconfigured to receive a signal to move the actuator so that thetransducer is moved relative to the disk; a spindle motor having aplurality of windings and a rotor rotatable at an operating spin-rateduring an operation mode of the disk drive; a spindle motor driverconnected to apply winding currents across a combination of the spindlemotor windings, and to receive a speed signal to enable measurement ofspindle motor speed; and a processor coupled to the VCM to apply asignal to measure a resistance of the VCM coil winding and provide atemperature estimate based on the measured resistance, the processorfurther coupled to receive the speed signal enabling measurement of thespindle motor speed, the processor providing a signal to the spindlemotor driver to turn off the spindle motor if the spindle motor speedhas not reached the operating spin-rate after a period of time, whereinthe period of time is increased with a decrease in the temperatureestimate provided from the processor; and a spindle motor controllercoupling the processor to the spindle motor driver, wherein the spindlemotor driver applies the winding currents to generate torque on therotor to cause movement of the spindle motor, and wherein the spindlemotor controller provides a signal to control a magnitude of the windingcurrents applied to increase the torque during startup corresponding tothe decrease in the temperature estimate provided from the processor. 2.The disk drive of claim 1, wherein the spindle motor controller isconfigured to identify a sequence of commutation states and sendcommutation voltage control signals to the spindle motor driver to applyvoltages across a selected combination of the windings of the spindlemotor to cause the sequence of commutation states resulting in torque onthe rotor to cause a desired movement of the spindle motor, wherein thespindle motor controller further provides a series of commutation clockpulses to advance the spindle motor driver between commutation states,and wherein the spindle motor controller controls timing of thecommutation clock pulses to increase the torque applied during startupcorresponding to the decrease in the temperature estimate provided bythe processor.
 3. The disk drive of claim 1, wherein the signal appliedto measure the resistance of the VCM coil winding is a set voltage, andthe resistance is determined from the resulting current received fromthe VCM coil winding.
 4. The disk drive of claim 1, wherein the signalapplied to measure the resistance of the VCM coil winding is a setcurrent, and the resistance is determined from the resulting voltageacross the VCM coil winding.
 5. The disk drive of claim 1, furthercomprising a memory connected with the processor, wherein processorreadable code is stored in the memory the code being readable to causethe processor to apply the signal to measure the resistance of the VCMcoil winding during startup, and to determine the temperature from atable of values stored in the memory with temperature corresponding tomeasured resistance.
 6. The disk drive of claim 1, further comprising amemory connected with the processor, wherein processor readable code isstored in the memory the code being readable to the processor to applythe signal to measure the resistance of the VCM coil winding duringstartup, and to determine the temperature based on a calculation usingthe measured resistance.
 7. A disk drive comprising: a rotatable disk;an actuator that supports a transducer; a voice control motor (VCM)including a coil winding configured to receive a signal to move theactuator so that the transducer is moved relative to the disk; a spindlemotor having a plurality of windings and a rotor rotatable at anoperating spin-rate during an operation mode of the disk drive; aspindle motor driver connected to apply winding currents across acombination of the spindle motor windings, and to receive a speed signalto enable measurement of spindle motor speed; and a processor coupled tothe VCM to apply a signal to measure a resistance of the VCM coilwinding and provide a temperature estimate based on the measuredresistance, the processor further coupled to receive the speed signalenabling measurement of the spindle motor speed, the processor providinga signal to the spindle motor driver to turn off the spindle motor ifthe spindle motor speed has not reached the operating spin-rate after aperiod of time, wherein the period of time is increased with a decreasein the temperature estimate provided from the processor; and a spindlemotor controller coupling the processor to the spindle motor driver, thespindle motor controller configured to identify a sequence ofcommutation states and send commutation voltage control signals to thespindle motor driver to apply voltages across a selected combination ofthe windings of the spindle motor to cause the sequence of commutationstates resulting in torque on the rotor to cause a desired movement ofthe spindle motor, wherein the spindle motor controller further providesa series of commutation clock pulses to advance the spindle motor driverbetween commutation states, and wherein the spindle motor controllercontrols timing of the commutation clock pulses to increase the torqueapplied during startup corresponding to the decrease in the temperatureestimate provided by the processor.
 8. A disk drive comprising: arotatable disk; a transducer; an actuator that supports the transducer;a voice control motor (VCM) connected to the actuator, the VCM includinga coil winding configured to receive a signal to move the actuator sothat the transducer is moved relative to the disk; a processor coupledto the VCM to apply a signal to measure a resistance of the VCM coilwinding, and to provide a temperature estimate based on the measuredresistance; a spindle motor having a plurality of windings and a rotorrotatable at an operating spin-rate during an operation mode of the diskdrive; a spindle motor driver connected to apply winding currents acrossa combination of the spindle motor windings; and a spindle motorcontroller coupling the processor to the spindle motor driver, whereinthe spindle motor driver applies the winding currents to generate torqueon the rotor to cause movement of the spindle motor, and wherein thespindle motor controller provides a signal to control a magnitude of thewinding voltages applied to increase the torque applied during startupcorresponding to a decrease in the temperature estimate provided fromthe processor.
 9. The disk drive of claim 8, wherein the spindle motorcontroller is configured to identify a sequence of commutation statesand send a signal to the spindle motor driver to apply voltages across aselected combination of the windings of the spindle motor to cause thesequence of commutation states resulting in torque on the rotor to causea desired movement of the spindle motor, wherein the spindle motorcontroller further provides a series of commutation clock pulses toadvance the spindle motor driver between commutation states, and whereinthe spindle motor controller controls timing of the commutation clockpulses to increase the torque applied during startup corresponding tothe decrease in the temperature estimate provided by the processor. 10.A disk drive comprising: a rotatable disk; a transducer; an actuatorthat supports the transducer; a voice control motor (VCM) connected tothe actuator, the VCM including a coil winding configured to receive asignal to move the actuator so that the transducer is moved relative tothe disk; a processor coupled to the VCM to apply a signal to measure aresistance of the VCM coil winding, and to provide a temperatureestimate based on the measured resistance; a spindle motor having aplurality of windings and a rotor rotatable at an operating spin-rateduring an operation mode of the disk drive; a spindle motor driverconnected to apply winding voltages across a combination of the spindlemotor windings; and a spindle motor controller coupling the processor tothe spindle motor driver, the spindle motor controller configured toidentify a sequence of commutation states and send a signal to thespindle motor driver to apply voltages across a selected combination ofthe windings of the spindle motor to cause the sequence of commutationstates resulting in torque on the rotor to cause a desired movement ofthe spindle motor, wherein the spindle motor controller further providesa series of commutation clockpulses to advance the spindle motor driverbetween commutation states, and wherein the spindle motor controllercontrols timing of the commutation clock pulses to increase the torqueapplied during startup corresponding to a decrease in the temperatureestimate provided by the processor.